This invention relates to the preparation of cyclopentadienyl or indenyl titanium trihalides.
Known methods for the synthesis, of cyclopentadienyl titanium trichlorides may require the use of titanium(III) trichloride, involve reduction-oxidation procedures, or the use of solvents, e.g., tetrahydrofuran (THF) or glyme, which are difficult to remove.
One such known synthesis entails treatment of pentamethyl cyclopentadiene with potassium tertiary butoxide to provide potassium pentamethyl cyclopentadiene which must then be treated with trimethyl silicon chloride (TMSCl) to obtain the desired pentamethyl cyclopentadienyl trichloride. The synthesis of the potassium pentamethyl cyclopentadiene results in a reaction mixture that contains tertiary butyl alcohol which is difficult to remove.
There is a need for an improved, cost effective synthesis of cyclopentadienyl and indenyl trichlorides which avoids these disadvantages.
A cyclopentadiene or indene is lithiated in THF or ethyl ether and treated with XTi (OiPr)3, wherein X is a halogen to produce a THF or ether solution of cyclopentadienyl or indenyl titanium tri-isopropoxide and a lithium halide. The THF or ethereal solvent is exchanged for a hydrocarbon solvent to precipitate the lithiumihalide which is separated by filtration. The mother liquor which contains cyclopentadienyl or indenyl titanium tri-isopropoxide is treated with SiCl4 or BCl3 to provide cyclopentadienyl or indenyl titanium trihalide.
In this specification, the expressions xe2x80x9ccyclopentadienexe2x80x9d and xe2x80x9cindenexe2x80x9d mean cyclopentadiene or indene per se or any alkyl cyclopentadiene or alkyl indene which has one or more, preferably C1 to C6 alkyl ring substituents. The ring substituents may be the same or different.
Pursuant to one embodiment of the invention, a cyclopentadiene or an indene is deprotonated with butyllithium in THF or similar solvent in which the lithiated cyclopentadiene or indene and the lithium chloride are each soluble. Useful solvents other than THF include diethyl ether and monoglyme. ClTi(OiPr)3, in which the expression xe2x80x9c(OiPr)xe2x80x9d means isopropoxide, is added to the deprotonated reaction mixture which is then heated, preferably at reflux, for 6 to 8 hours to provide a second reaction mixture that contains a cyclopentadienyl or indenyl titanium tri-isopropoxide and lithium chloride.
The reaction mixture solvent is exchanged for an aliphatic hydrocarbon solvent, e.g., Isopar(copyright)E, to precipitate the LiCl which is removed by filtration.
The filtrate, a solution of a cyclopentadienyl or indenyl titanium tri-isopropoxide, is treated with SiCl4, AlCl3 or BCl3, preferably at reflux in an amount at least stoichiometrically appropriate, to provide the corresponding cyclopentadiene titanium trichloride.
Any compound of the formula XTi (OR)3, in which X is a halogen, preferably chlorine, and R is an alkyl group, preferably a C1 to C6 alkyl group, may be used instead of ClTi (OiPr)3.